Intel's Glass Substrates Advancements Could Revolutionize Multi-Chiplet Packages

Intel today formally confirmed that it would use glass substrates for advanced packaging in the second half of this decade. Intel expects superior mechanical, physical, and optical properties of glass substrates to enable the company to build higher-performance multi-chiplet system-in-packages (SiPs), aimed primarily at data centers. In particular, Intel expects glass substrates to enable ultra-large 24×24 cm SiPs housing multiple pieces of silicon.

Glass offers a range of benefits over traditional organic substrates. Among its standout features is its ultra-low flatness for improved depth of focus for lithography, as well as superior dimensional stability for interconnects. This will be important for next-generation SiPs with even more chiplets compared to today's devices, like Intel's own Ponte Vecchio. Such substrates also provide superior thermal and mechanical stability, which allows them to endure higher temperatures, making them more resilient in data center applications. 

In addition, Intel says that glass substrates allow for a much higher interconnect density (i.e., tighter pitches), making it possible for a tenfold increase in this aspect, which is crucial for power delivery and signal routing of next-generation SiPs. In particular, Intel is talking about <5/5um Line/Space and <100um through-glass via (TGV) pitch, which enables die-to-die bump pitch of <36um on substrate and core bump pitch <80um. Furthermore, glass substrates reduce pattern distortion by 50%, which improves focus depth for lithography and ensures more precise and accurate semiconductor manufacturing. 

The introduction of glass substrates by Intel is a significant leap from organic substrates that are used currently by the industry. The world's largest supplier of processors believes that organic substrates will reach the limits of their capabilities in the coming years, as the company will produce data center-oriented SiPs with tens of tiles and perhaps thousands of watts of power consumption. Such SiPs would require very dense interconnections between chiplets, while ensuring the whole package does not bend during production or over the time it's in use because of heat.

Since such SiPs do not exist today, glass substrates are not just about overcoming challenges like interconnect densities and temperature tolerance. They enable Intel to build game-changing solutions for data centers, AI, and graphics, the company says. This could set the stage for achieving a staggering 1 trillion transistors on a single package within the next decade.

For now at least, Intel is the only chip maker that is talking about glass substrates, and there could be a reason for that. The company says that it has been working on this technology for about a decade, and now it has a fully integrated glass R&D line in its Chandler, Arizona, campus, where the company develops packaging technologies. Intel says that the line cost it over $1 billion and to make it work, it needed to collaborate with both equipment and materials partners. Just a few companies in the industry can afford such investments, and Intel appears to be the only company that has developed glass substrates so far.

To prove that the technology works, Intel released a fully-functional test chip that uses 75um TGVs with a 20:1 aspect ratio, as well as a 1 mm core thickness. While the test chip is a client device, the technology will be initially be used to build data center-oriented processors. But after the tech gets more mature, it will be used for client computing applications. Intel mentioned graphics processors among possible applications for the technology, and since GPUs can consume whatever number of transistors thrown at them, it is likely that they will benefit from the increased interconnection density and improved rigidity of glass substrates.

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